Chalcogenide compounds for the remediation of nuclear and heavy metal wastes

ABSTRACT

Chalcogenide compounds, including ternary and quaternary tin and antimony chalcogenides, for use as absorbents in the remediation of hazardous materials are provided. Also provided are methods for using the chalcogenides in the remediation of ionic and elemental metals from aqueous and non-aqueous fluids.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority from U.S. provisional patentapplication No. 61/347,903, filed on May 25, 2010, the entire disclosureof which is incorporated herein by reference.

STATEMENT OF GOVERNMENT RIGHTS

This invention was made with government support under grant numberDMR-0801855 awarded by the National Science Foundation. The governmenthas certain rights in the invention.

BACKGROUND

The disposal of nuclear waste discharged with the spent fuel from afission nuclear power plant is one of the most important environmentalsafety issues faced by the nuclear power industry. This issue ishindering the use of nuclear power in a safe, abundant, efficient, andproliferation-resistant manner. Isotopes responsible for the majority ofthe external gamma exposure in fuel reprocessing plants are ¹³⁷Cs and⁹⁰Sr in the form of dissolved ions. High level waste (HLW) containsprimarily the fission radionuclides ¹³⁷Cs and ⁹⁰Sr and very smallamounts of transuranic radionuclides. (See, “Development of matrices forvitrification of strontium and cesium concentrate from high-levelwaste”; Aloi, A. S.; Trofimenko, A. V.; Iskhakova, O. A.; Kolycheva, T.I.; Radiochemistry 1997, 39, 567-573; “Cesium removal demonstrationusing selected actual waste samples from the Hanford reservation tankfarm”; Peterson, R. A.; Fiskum, S. K.; Arm, S. T.; Blanchard, D. L.;Separation Science and Technology 2006, 41, 2361-2371; and“Demonstration of the caustic-side solvent extraction process for theremoval of (CS)—C-137 from Savannah River Site high level waste”;Norato, M. A.; Beasley, M. H.; Campbell, S. G.; Coleman, A. D.; Geeting,M. W.; Guthrie, J. W.; Kennell, C. W.; Pierce, R. A.; Ryberg, R. C.;Walker, D. D.; Law, J. D.; Todd, T. A.; Separation Science andTechnology 2003, 38, 2647-2666.) Various processes exist to convert HLWinto a variety of forms including alkaline or acidic supernatant liquid,sludge, salt cake, or calcine solid, however, further improvements andbreakthroughs are necessary to resolve this issue.

Cesium is often removed from waste waters in the nuclear industry bymeans of solid ion-exchangers, ranging from organic polymers (see, “Theuniversal solvent extraction (UNEX) process. II. Flowsheet developmentand demonstration of the UNEX process for the separation of cesium,strontium, and actinides from actual acidic radioactive waste”; Law, J.D.; Herbst, R. S.; Todd, T. A.; Romanovskiy, V. N.; Babain, V. A.;Esimantovskiy, V. M.; Smirnov, I. V.; Zaitsev, B. N.; Solvent Extractionand Ion Exchange 2001, 19, 23-36; and “Selective transport of cesium andstrontium ions through polymer inclusion membranes containingcalixarenes as carriers”; Arena, G.; Contino, A.; Magri, A.; Sciotto,D.; Lamb, J. D.; Supramolecular Chemistry 1998, 10, 5-15), compounds(see, “Decontamination of high-level waste using a continuousprecipitation process”; Peterson, R. A.; Burgess, J. O.; Walker, D. D.;Hobbs, D. T.; Serkiz, S. M.; Barnes, M. J.; Jurgensen, A. R.; SeparationScience and Technology 2001, 36, 1307-1321) and macrocycles (see, “Arobust alkaline-side CSEX solvent suitable for removing cesium fromSavannah River high level waste”; Bonnesen, P. V.; Delmau, L. H.; Moyer,B. A.; Leonard, R. A.; Solvent Extraction and Ion Exchange 2000, 18,1079-1107; and “Actinide, strontium, and cesium removal from Hanfordradioactive tank sludge”; Lumetta, G. J.; Wagner, M. J.; Carlson, C. D.;Solvent Extraction and Ion Exchange 1996, 14, 35-60) to inorganic solidssuch as zeolites (see, “The effect of amorphization on the Cs ionexchange and retention capacity of zeolite-NaY”; Gu, B. X.; Wang, L. M.;Ewing, R. C.; Journal of Nuclear Materials 2000, 278, 64-72; “Ionexchange selectivity of phillipsite for Cs and Sr as a function offramework composition”; Adabbo, M.; Caputo, D.; de Gennaro, B.; Pansini,M.; Colella, C.; Microporous and Mesoporous Materials 1999, 28, 315-324;“The removal of strontium and cesium from simulated hanford groundwaterusing inorganic ion exchange materials”; Sylvester, P.; Clearfield, A.;Solvent Extraction and Ion Exchange 1998, 16, 1527-1539; “AdsorptionBehavior of Cesium and Strontium on Synthetic Zeolite-P”; Mimura, H.;Akiba, K.; Journal of Nuclear Science and Technology 1993, 30, 436-443;“Removal of Heat-Generating Nuclides from High-Level Liquid Wastesthrough Mixed Zeolite Columns”; Mimura, H.; Akiba, K.; Igarashi, H.;Journal of Nuclear Science and Technology 1993, 30, 239-247; and“Distribution and Fixation of Cesium and Strontium in Zeolite-a andChabazite”; Mimura, H.; Kanno, T.; Journal of Nuclear Science andTechnology 1985, 22, 284-291).

Inorganic ion exchangers possess a number of advantages as Sr²⁺ and Cs⁺adsorbents over conventional organic ion-exchange resins, includingsuperior chemical, thermal and radiation stability. (See, “Ion exchangeproperties of a cesium ion selective titanosilicate”; Bortun, A. I.;Bortun, L. N.; Clearfield, A.; Solvent Extraction and Ion Exchange 1996,14, 341-354; and “Highly selective inorganic crystalline ion exchangematerial for Sr²⁺ in acidic solutions”; Nenoff, T. M.; Miller, J. E.;Thoma, S. G.; Trudell, D. E.; Environmental Science & Technology 1996,30, 3630-3633). Because the primary chemical components of alkalinesupernatants are sodium nitrate and sodium hydroxide, the majority ofthese could be disposed of as low level waste if radioactive ¹³⁷Cs couldbe selectively removed. However, recovery of long lived radionuclidesfrom waste solutions containing large concentrations of salt has been achallenging task. Up to now solutions based on organic crown ethers (andmacrocycles) and inorganic oxide ion-exchange materials (such as clays,zeolites, alkali metal titanium silicates, manganese oxides, etc.),liquid ionic technologies have been tested and have been moderatelyeffective. (See, “The effect of amorphization on the Cs ion exchange andretention capacity of zeolite-NaY”; Gu, B. X.; Wang, L. M.; Ewing, R.C.; Journal of Nuclear Materials 2000, 278, 64-72; “Selective exchangeand fixation of strontium ions with ultrafine Na-4-mica”; Kodama, T.;Harada, Y.; Ueda, M.; Shimizu, K.; Shuto, K.; Komarneni, S.; Langmuir2001, 17, 4881-4886; “Sorption of Am(III), U(VI) and Cs(I) on sodiumpotassium fluorophlogopite, an analogue of the fluorine mica mineral”;Saxena, A.; Tomar, R.; Murali, M. S.; Mathur, J. N.; Journal ofRadioanalytical and Nuclear Chemistry 2003, 258, 65-72; “Separation ofcesium and strontium by potassium nickel hexacyanoferrate(II)-loadedzeolite A”; Mimura, H.; Kimura, M.; Akiba, K.; Onodera, Y.; Journal ofNuclear Science and Technology 1999, 36, 307-310; “Integratedexperimental and computational methods for structure determination andcharacterization of a new, highly stable cesium silicotitanate phase,Cs₂TiSi₆O₁₅ (SNL-A)”; Nyman, M.; Bonhomme, F.; Teter, D. M.; Maxwell, R.S.; Gu, B. X.; Wang, L. M.; Ewing, R. C.; Nenoff, T. M.; Chemistry ofMaterials 2000, 12, 3449-3458; “Chromatographic-Separation of Strontiumand Cesium with Mixed Zeolite Column”; Mimura, H.; Kobayashi, T.; Akiba,K.; Journal of Nuclear Science and Technology 1995, 32, 60-67;“Separation of Heat-Generating Nuclides from High-Level Liquid Wastesthrough Zeolite Columns”; Mimura, H.; Akiba, K.; Journal of NuclearScience and Technology 1994, 31, 463-469; “Titanium silicates,M₃HTi₄O₄(SiO₄)₃4H₂O (M=Na⁺, K⁺), with three-dimensional tunnelstructures for the selective removal of strontium and cesium fromwastewater solutions”; Behrens, E. A.; Clearfield, A.; MicroporousMaterials 1997, 11, 65-75; “Syntheses, crystal structures, andion-exchange properties of porous titanosilicates, M₃HTi₄O₄(SiO₄)₃4H₂O(M=H⁺, K⁺, Cs⁺), structural analogues of the mineral pharmacosiderite”;Behrens, E. A.; Poojary, D. M.; Clearfield, A.; Chemistry of Materials1996, 8, 1236-1244; “Sorption behavior of radionuclides on crystallinesynthetic tunnel manganese oxides”; Dyer, A.; Pillinger, M.; Newton, J.;Harjula, R.; Moller, T.; Amin, S.; Chemistry of Materials 2000, 12,3798-3804; and “Layered metal sulfides: Exceptionally selective agentsfor radioactive strontium removal”; Manos, M. J.; Ding, N.; Kanatzidis,M. G.; Proceedings of the National Academy of Sciences of the UnitedStates of America 2008, 105, 3696-3699.) There are, however, drawbacksto these approaches including cost, stability and selectivity.

The compounds A_(2x)M_(x)Sn_(3-x)S₆ (x=0.1-0.95; A=Li⁺, Na⁺, K⁺, Rb⁺;M=Mn²⁺, Mg²⁺, Zn²⁺, Fe²⁺) (e.g., “KMS”) have been reported as agents forradioactive strontium removal. (See, “Layered metal sulfides:Exceptionally selective agents for radioactive strontium removal”;Manos, M. J.; Ding, N.; Kanatzidis, M. G.; Proceedings of the NationalAcademy of Sciences of the United States of America 2008, 105,3696-3699.) However, it would be helpful to have additional compoundsfor remediation applications.

Like nuclear waste, heavy metal contamination in water poses asignificant environmental hazard. Mercuric (Hg²⁺) and other soft heavymetal ions such as Cd²⁺ and Pb²⁺ represent major contaminants in naturalwater sources and industrial waste water and constitute a threat forhumans and other species. (See, T. W. Clarkson in Heavy metals in theenvironment (Ed.: B. Sarkar) Marcel Dekker Inc., 2002, pp. 457-502.)Conventional ion-exchangers such as zeolites and clays and adsorbents,such as activated carbon generally have low selectivity and weak bindingaffinity for soft metal ions. (See, G. Blanchard, M. Maunaye, G. Martin,Water Res. 1984, 18, 1501-1507; A. Benhammou, A. Yaacoubi, L. Nibou, B.Tanouti, J. Colloid. Interface Sci. 2005, 282, 320-326; and C. P. Huang,D. W. Blankenship, Water Res. 1984, 18, 37-46.) Thiol-functionalizedadsorbents, including clays, resins, organoceramics and mesoporoussilicates, are considered the most effective sorbents for soft heavymetal ions and in particular for Hg²⁺. (See, R. Celis, M. C. Hermosin,J. Cornejo, Environ. Sci. Technol. 2000, 34, 4593-4599; I. L. Lagadic,M. M. Mitchell, B. D. Payne, Environ. Sci. Technol. 2001, 35, 984-990;S. Chiarle, M. Ratto, M. Rovvati, Water Res. 2000, 34, 2971-2978; D.Kara, Anal. Let. 2005, 38, 2217-2230; A. M. Nam, L. L. Tavlarides,Solvent Extract. Ion. Exch. 2003, 21, 899-913; J. S. Lee, S.Gomez-Salazar, L. L. Tavlarides, React. Funct. Polym. 2001, 49, 159-172;A. M. Nam, S. Gomez-Salazar, L. L. Tavlarides, Ind. Eng. Chem. Res.2003, 42, 1955-1964; X. Feng, G. E. Fryxell, L.-Q. Wang, A. Y. Kim, J.Liu, K. M. Kemner, Science 1997, 276, 923-926; J. Liu, X. Feng, G. E.Fryxell, L.-Q Wang, A. Y. Kim, M. Gong, Adv. Mater. 1998, 10, 161-165;X. Chen, X. Feng, J. Liu; G. E. Fryxell, M. Gong, Sep. Sci. Technol.1999, 34, 1121-1132; L. Mercier, T. J. Pinnavaia, Adv. Mater. 1997, 9,500-503; L. Mercier, T. J. Pinnavaia, Environ. Sci. Technol. 1998, 32,2749-2754; J. Brown, L. Mercier, T. J. Pinnavaia, Chem. Commun. 1999,69-70; C.-C Chen, E. J. McKimmy, T. J. Pinnavaia, K. F. Hayes, Environ.Sci. Technol. 2004, 38, 4758-4762; S. J. L. Billinge, E. J. McKimmy, M.Shatnawi, H. Kim, V. Petkov, D. Wermeille, T. J. Pinnavaia, J. Am. Chem.Soc. 2005, 127, 8492-8498; J. Brown, R. Richer, L. Mercier, Microp.Mesop. Mater. 2000, 37, 41-48; L. Mercier, C. Detellier, Environ. Sci.Technol. 1995, 29, 1318-1323.) In addition, mesoporous carbon materialswith thiopyrene functional groups were proven to be excellent sorbentsfor mercuric ions. (See, Y. S. Shin, G. Fryxell, W. Y. Um, K. Parker, S.V. Mattigod, R. Skaggs, Adv. Funct. Mater. 2007, 17, 2897-2901.) Morerecently, iron oxide nanoparticles coated with humic acid showedremarkable capability to remove heavy metal ions (Hg²⁺, Pb²⁺, Cd²⁺,Cu²⁺) from water. (See, J.-F. Liu, Z.-S Zhao, G.-B. Jiang, Environ. Sci.Technol. 2008, 42, 6949-6954.) However, additional and improved wastewater remediation compounds for heavy metal contamination are desired.

Crude oil and unprocessed gas can contain significant amounts ofelemental mercury and chemically bound mercury. Raw produced hydrocarbonliquids also contain organic mercury compounds that partition intoparticular product streams in distillations and separations. Mercury isharmful to petroleum handling and processing systems because in gasprocessing, mercury can damage equipment, including cryogenic heatexchangers. Also, mercury poisons catalysts and becomes a component ofwaste water, which negatively impacts regulatory compliance. (SeeWilhelm, S M; Bloom, N Fuel Processing Technology 2000, 63, 1-27;Wilhelm S M, Liang L, Cussen D, et al. Environmental Science &Technology, 2007, 41, 4509-4514).

Crude oil typically contains several chemical species of mercury, whichdiffer in their chemical and physical properties. These includeelemental mercury, organic mercury compounds (e.g., R₂Hg and RHgX, whereR═CH₃, C₂H₅, etc., and X═Cl⁻, etc.) and salts of the Hg²⁺ ion. Thelatter are soluble in oil and gas condensate but preferentiallypartition into the water phase in primary separations. Mercuricchlorides and halides have a reasonably high solubility in organicliquids (order of magnitude more than elemental mercury). (Bloom, N. S.Fresenius' J. Anal. Chem. 2000, 366(5):438. Wilhelm, S., and N. Bloom.Fuel Proc. Technol. 2000, 63:1).

SUMMARY

The present invention provides methods for the remediation of fluidsamples. The methods comprise exposing a fluid sample comprising metalions to an ion exchange medium comprising a chalcogenide compound havingthe formula (A_(x)B_(x′))M_(y)Q_(z), where A is an alkali cation or analkylammonium cation; B is an alkaline earth cation; M is Sn, Zn, P, Cuor Sb; and Q is S or Se, wherein the values of x, y and z can be thesame or different; x, x′ and y can range, independently, from 0 to 9,provided that if one of x and x′ is zero, the other is not; and z canrange from 1 to 25. In the present methods, the chalcogenide compoundsabsorb the metal, which can then be removed from the fluid sample.

The chalcogenide compounds can be used to remove a variety of metal ionsfrom a fluid (e.g., liquid or gas) sample, including ions of metals thatpose an environmental and/or health risk. Thus, examples of fluidsamples that can be remediated by the present methods include, wastewater generated from a nuclear reactor or an industrial plant. Examplesof metal ions that can removed from the liquid samples includeradionuclide ions, such as isotopes of Cs and Sr (e.g., ¹³⁷Cs and ⁹⁰Sr),and heavy metal ions, such as mercury, lead, cadmium, cobalt, nickel,copper, gold, silver, platinum, palladium, and thallium ions. Inaddition, the chalcogenide compounds can be used to remove elementalmetals, such as mercury, from a fluid sample, such as ahydrocarbon-based liquid or gas.

The amount of metal removed from the fluid sample will depend on theinitial concentration of the metal in the sample, the amount ofchalcogenide compound in the absorption medium, the nature of the metaland the chalcogenide compounds, and/or the time of exposure. In someembodiments of the present methods, at least 50 percent by weight of themetal is removed from the sample. This includes embodiments in which atleast 70 percent by weight, at least 90 percent by weight, and at least99 percent by weight of the metal is removed from the sample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. (a) is a diagram of a part of the layer framework of K₂Sn₄S₉(“KTS-1”) viewed down the c-axis. The Sn and S atoms are represented bylight gray (tetrahedrally coordinated) and darker gray ballsrespectively; (b) is a diagram of the structure, with a polyhedralrepresentation of the layers, along the b-axis. Disordered K⁺ ions(black balls) are hosted in the interlayer and pore spaces.

FIG. 2. (a) shows a part of the layer framework of K₂Sn₂S₅ (“KTS-2”)viewed down the b-axis. The Sn and S atoms are represented by dark grayand medium gray balls respectively; (b) is a diagram of the structure,with a polyhedral representation of the pore structure. K⁺ ions (larger,light gray balls) are hosted in the pore spaces in both (a) and (b).

FIG. 3. Shows the equilibrium absorption capacity (q) data for Cs⁺ ionexchange with K₂Sn₄S₉ (pH≈7, V/m 1000 mL/g, exposure time ˜12 h, initialCs⁺ concentrations in the range 34 ppm to 347 ppm, in accordance withExample 1, below). The solid lines represent the fitting of the datawith the models presented in Example 1.

FIG. 4. Shows the Log of K_(d) values as a function of initial Csconcentration, in accordance with Example 1, below. These are veryhigh—in the range of 1.3×10³-2.5×10⁵ mL/g, which demonstrates theusefulness of KTS-1 for Cs⁺ ion-exchange.

DETAILED DESCRIPTION

The present invention relates to compounds for the use as absorbents forthe remediation of various hazardous materials. More specifically, thepresent invention relates to the use of ternary and quaternarychalcogenides, including tin and antimony chalcogenides, as absorbentsin remediation applications. In some embodiments, the compounds can beused as ion exchange materials for absorbing metal ions, including heavymetal ions from aqueous or non-aqueous fluids, such as waste waterstreams. Metal ions that can be exchanged with the present chalcogenidesinclude Cs⁺, Hg²⁺, MeHg²⁺, Cd²⁺, Pb²⁺, Co²⁺, Ni²⁺, Cu²⁺, Pt²⁺, Pd²⁺,Sr²⁺, Au⁺, Ag⁺ and Tl⁺ ions. In other embodiments, the compounds can beused to remove elemental metals, such as mercury, from aqueous ornon-aqueous fluids, including hydrocarbon fluids such as petroleum,crude oil or natural gas (methane).

The chalcogenides can be represented by the formula:(A_(x)B_(x′))M_(y)Q_(z), where A is an alkali cation or an alkylammoniumcation; B is an alkaline earth cation; M is Sn, Zn, P, Cu or Sb; and Qis S or Se. The x, y and z can be the same or different and x and y canrange from 0 to 9, provided that if one of x and x′ is zero, the otheris not. The value of z can range from 1 to 25; For example, A can be Li,Na, K, Rb, Cs, or [R_(4-x)NH_(x)]⁺, where R=an alkyl group, such asmethyl, ethyl, propyl, butyl, and the like, and B can be Mg, Ca, Sr, orBa. The compounds contain many differing structure types, includinglayered and porous materials having a three dimensional open-framework.When used to remove ions from aqueous waste, these materials can havecomparable or better performance and selectivity than benchmarkmaterials, such as ion-exchange resins and functionalized silicas,zeolites and clays.

In one embodiment of the present invention, the compounds have theformula A_(x)M_(y)Q_(z) (i.e., x′=0), where x and y can range from 1 to9 (e.g., from 2 to 9) independently and z can range from 1 to 20. Theselectivity of A_(x)M_(y)Q_(z) compounds can be attributed to theirchalcogenide surfaces, which have much larger binding affinities forsofter ions than those of the traditional oxide frameworks. The presenceof the soft chalcogen ligands of the chalcogenides can induce innateselectivity for softer heavier metal ions and against hard ions such asNa²⁺ or Ca²⁺. In addition, the pores in some of the structures caninfluence the selectivity of one ion over the other. These propertiesare particularly useful for ion discrimination in nuclear wastes orwaste water with heavy metal ion contaminants.

Non-limiting examples of tin and antimony chalcogenide compounds fallingwithin this category include those having the formulas: A₂Sn₂Q_(z),where z is in the range from 6 to 20; A₂Sn₄Q_(z), where z is in therange from 10 to 19; A₂Sb₄Q_(z), where z is in the range from 8 to 22;and A₂Sb₈Q_(z), where z is in the range from 14 to 23. Non-limitingexamples of phosphorus chalcogenide compounds falling within thiscategory include those having the formulas: A₂P₂Q_(z), where z is in therange from 7 to 21; and APQ_(z), wherein z is in the range from 7 to 16.

Two specific embodiments of the present chalcogenide compounds that canbe used to illustrate, but not to limit, the present invention areK₂Sn₄S₉ and K₂Sn₂S₅. K₂Sn₄S₉ is an example of a layered material thatundergoes ion-exchange with several ions. The structure of K₂Sn₄S₉ isshown in FIGS. 1( a) and 1(b). As shown in these figures, edge sharingand corner sharing SnS₄ tetrahedra, where the S atoms are alwaysthree-coordinated, build up the layer. The A⁺ ions intercalated betweenthe layers are positionally disordered and easily exchangeable for avariety of cations.

The basic building block of these layers is the Sn₄S₉ cluster which iscomposed of two tetrahedral SnS₄ and two trigonal pyramidal SnS₃ unitsfused into the larger unit through edge- or corner-sharing of sulfuratoms. These Sn₄S₉ clusters associate into layers by coordinating toeach other via intercluster Sn—S bonds. Each Sn₄₅₉ fragment is connectedto four others in a nearly face-centered arrangement through (μ-S)₂bridges forming the overall [Sn₄S₉]²⁻ layer found in both compounds. Theintercluster Sn—S bonds give rise to the observed five-coordinate aswell as tetrahedral tin centers in the layer (FIG. 1).

K₂Sn₂S₅ (“KTS-2”) features only five-coordinate Sn centers, as shown inthe structures of FIGS. 2( a) and 2(b). The anionic framework has SnS₅distorted trigonal bi-pyramids as building blocks which share two oftheir common edges (formed by an axial S atom and an equatorial S atom)with one another to form [SnS₃]_(n) ^(2n−) chains running in thedirection of [110] and [1-10], alternately. The [SnS₃]_(2n) ^(2n−)chains are cross-linked by sharing the remaining equatorial S atoms ofthe trigonal bipyramids to form an extended three-dimensional framework.The (Sn₂S₅)²⁻ framework features 1D tunnels running parallel to theb-axis. These tunnels contain the K⁺ atoms (FIG. 2).

Examples of other ternary sulfides having selective ion exchangeproperties are (a) A₂Sn₃S₇ compounds (A=Li, Na, K, Rb, Cs, or[R_(4-x)NH_(x)]⁺, where R=an alkyl group, such as methyl, ethyl, propyl,butyl, and the like) and (b) A₂Sb₄S₇, (A=Li, Na, K, Rb, Cs, or[R_(4-x)NH_(x)]⁺, where R=an alkyl group, such as methyl, ethyl, propyl,butyl, and the like.

Specific, non-limiting examples of ternary tin and antimonychalcogenides having the structure A_(x)M_(y)Q_(z) include K₂Sn₄S₁₀,Na₂Sn₄S₉, Na₂Sn₄S₁₀, K₂Sn₄S₁₁, K₂Sn₄S₁₂, K₂Sn₄S₁₃, K₂Sn₄S₁₄, K₂Sn₄S₁₆,K₂Sn₂S₆, K₂Sn₂S₇, K₂Sn₂S₈, K₂Sn₂S₁₀, K₂Sn₂S₁₄, and K₂Sn₂S₂₀; K₂Sb₈S₁₃,K₂Sb₄S₇, Na₂Sb₈S₁₃, Na₂Sb₄S₇, K₂Sb₈S₁₅, K₂Sb₄S₁₀, K₂Sb₈S₁₈, K₂Sb₄S₉,K₂Sb₈S₂₀, and K₂Sb₄S₂₀. Other ternary chalcogenides having thisstructure include KPS₇, K₂P₂S₈, KPS₁₀, K₂P₂S₁₀, NaPS₈, Na₂P₂S₁₂,NaPSe₁₂, and Na₂P₂Se₈; K₄Cu₂S₈, KCuS₅, K₄Cu₂S₁₀, KCuS₇, K₄Cu₂Se₈,KCuSe₅, K₄Cu₂Se₁₀, and KCuSe₇; K₄Zn₂S₈, K₂ZnS₄, K₄Zn₂S₁₀, and K₂ZnS₆.

In some embodiments of the present invention, the compounds have theformula B_(x)M_(y)Q_(z), where x and y can range from 1 to 9 (e.g., from2 to 9) independently and z can range from 1 to 25. Certain categorieswithin this group have x values or 1 or 2, y values in the range of 2 to4, and z values in the range of 6 to 10. This class of compoundsincludes chalcogenides having the following formulas: B₂Sn₂Q_(z), wherez can range from 7 to 21; BSn₂Q_(z), wherein z can range from 6 to 20;BSn₄Q_(z), where z can range from 10 to 19; B₂SnQ_(z), where z can rangefrom 5 to 24; BZnQ_(z), where z can range from 3 to 17; and B₂Sb₂Q_(z),where z can range from 6 to 25.

Specific, non-limiting examples of ternary tin and antimonychalcogenides having the structure B_(x)M_(y)Q_(z) include CaSn₃S₇;CaSb₄S₇; Ca₂Sn₂S₆; Mg₂Sn₂S₆; Ca₂Sn₂S₆; Ca₂Sn₂S₈; and Ca₂Sn₂S₁₀.

In some embodiments of the present invention, the compounds have theformula (A_(x)B_(x′))M_(y)Q_(z), where x, x′, and y can range from 1 to9 (e.g., from 2 to 9) independently and z can range from 1 to 25.Certain categories within this group have x values of 4, x′ values of 2,y values of 4, and z values of 12. Specific, non-limiting examples ofternary tin and antimony chalcogenides having the structure(A×Bx′)M_(y)Q_(z) include K₄Mg₂Sn₄S₁₂; Na₄Mg₂Sn₄S₁₂; Na₄Ca₂Sn₄S₁₂; andK₄Ca₂Sn₄S₁₂.

The present compounds can be used as ion exchangers in nuclear wastemanagement facilities. They can be also used for purification of wastewater from industries producing electric lamps, gauges, batteries,chemicals, thermometers, and paper, as well as from mines where Hg isextracted (usually as HgS). In addition, they can be used by companiesproducing filters for the purification of drinking water. The spentmercury and heavy metal absorbents can be recycled through standardmetal smelters.

In addition to removing metal ions from aqueous and non-aqueous fluids,the present compounds can be used to remove elemental metals fromaqueous and non-aqueous fluids, such as from hydrocarbon-based liquidsand gases. In some embodiments, the compounds can be used to removeelemental mercury from a liquid or a gas sample. This includedembodiments in which chalcogenide-rich compounds are used tosimultaneously remove heavy metal ions and elemental metal from a liquidor gas hydrocarbon sample. In these embodiments, the ionic metals andthe elemental metals may be the same or different. By way ofillustration only, the simultaneous removal of ionic and elementalmercury can be accomplished as follows:

K₂Sn₄S₈+Hg_((elemental))+Hg_((ionic))²⁺→Hg_((ionic))[Sn₄S₈(Hg_((elemental)x)]+2K⁺

K₂Sb₄S₁₀+Hg_((elemental))+Hg_((ionic))²⁺→Hg_((ionic))[Sb₄S₁₀(Hg_((elemental)x)]+2K⁺

Ca₂Sn₄S₁₄+Hg_((elemental))+Hg_((ionic))²⁺→(Hg_((ionic)))₂[Sn₄S₁₄(Hg_((elemental)x)]+2Ca²⁺

Without being limited by a specific form, the chalcogenide materials canbe used in a packed bed column or filter configuration. The purpose of apacked bed is typically to improve contact between two phases in achemical or similar process. In this embodiment of chemical processingusing the chalcogenide materials a packed bed can be a hollow tube,pipe, or other vessel that is filled with the chalcogenide materials andother support materials. The chalcogenide materials can be inparticulate form, pelletized form or supported on an inert support.

Certain embodiments of the present compounds and their use in hazardouselement remediation are illustrated in the following examples.

EXAMPLES

The following examples illustrate the use of the present chalcogenidecompounds in metal remediation applications.

Example 1 Remediation of Cs⁺ by K₂Sn₄S₉

Materials and Methods.

The chalcogenides were made by combining the potassium, tin and sulfur(or K₂ and SnS₂) in stoichiometric amounts and melting the resultingmixture at 500 to 700° C. Methods for making K₂Sn₄S₉ are described ingreater detail in Marking et al., J. Solid State Chem. 1998, 141, 17-28,the entire disclosure of which is incorporated herein by reference.

Powder patterns were obtained using a CPS 120 INEL X-ray powderdiffractometer with Ni-filtered Cu Kα radiation operating at 40 kV and20 mA and equipped with a position-sensitive detector. Samples wereground and spread on a glass slide.

The ion-exchange experiments were carried out with the batch method. Atotal of 10 mg of KTS-1 was weighted into a 20 ml glass vial. A 390 ppmsolution of Cs⁺ was made by weighing out 49.78 mg of CsCl and dilutingit into a 100 mL volumetric flask with deionized water; 10 mL of thiswas added to the glass vial. For subsequent reactions, the initial Cs⁺concentration (C_(o)) was diluted by combining x mL of 390 ppm Cs⁺solution to y mL of deionized water in the vial where x+y=10 mL. To eachvial a magnetic stir bar was added and the reactions were stirredovernight between 10-15 hours. The stir bars were then removed, and thevials were centrifuged (3980 rpm for 20 minutes). The supernatant wasdecanted into a centrifuge tube through a filter to collect any excessparticles. The centrifuge tube was then centrifuged again (3980 rpm for20 minutes) and the supernatant was removed by pipette into a new,labeled centrifuge tube for analysis. The determination of the ioniccontent of the solutions after the ion exchange processes (C_(e)) wereconducted by Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS).Standards in the range 1-40 ppb were prepared. Each experiment wasperformed in triplicate. The reactions with potable water samples, towhich trace concentrations of Cs were added, were carried out similarlyas the reactions with the neutral solutions. The results of the ionexchange studies are shown in Table 1 and the measured exchangecapacities are shown in FIG. 3.

TABLE 1 Ion-Exchange of K₂Sn₄S₉ with Cs⁺ (V/m = 1000 mL/g, Reaction time~15 hrs). Exchange % Cs⁺ Capacity, q Removal (mg Cs/g Sample C_(o) (ppb)C_(e) (ppb) (by weight) K_(d) (mL/g) KTS-1) 1 34375 132.5 99.6 25843434.2 2 68750 1162.5 98.3 58140 67.6 3 103125 3067.5 97 32619 100.1 4138750 5805 95.8 22902 132.9 5 173438 19570 88.7 7862 153.9 6 20812536375 82.5 4722 171.8 7 242813 55287.5 77.2 3392 187.5 8 277500 82962.570.1 2344 194.5 9 312188 97325 68.8 2208 214.9 10 346875 147000 57.61360 199.9 11 393375 201500 48.8 952 191.9 12 393375 183125 53.5 1148210.3 13 393375 167000 57.6 1356 226.4

Maximum initial Cs concentration used corresponded to ˜2.6 equivalentsin relation to K₂Sn₄S₉. Model exchange capacities for the compounds(solid lines in FIG. 3) were calculated using Langmuir-Freundlich andLangmuir equations as shown below:

Equation Langmuir-Freundlich:

$q = {q_{m}\frac{\left( {bC}_{e} \right)^{\frac{1}{n}}}{1 + \left( {bC}_{e} \right)^{\frac{1}{n}}}}$

Adj. R-Square 0.966, q_(m)=243(23) mg/g; b=0.18(8) L/mg; n=1.9(4).

Equation Langmuir:

$q = {q_{m}\frac{{bC}_{e}}{1 + {bC}_{e}}}$

Adj. R-Square 0.931; q_(m)=205(6) mg/g; b=0.32(7) L/mg.

The theoretical absorption capacity for exchange of all K by Cs is equalto 316 mg Cs/g of KTS-1. The maximum experimental absorption capacityfound was ˜205-243 mg, i.e. the ⅔ of the theoretical capacity. Thismeans that ˜70% of all K can be exchanged by Cs.

FIG. 4 shows the log K_(d) values as a function of the initial Csconcentration.

Compared to KMS-1, KTS-1 has similar exchange capacity but higheraffinity for Cs (higher K_(d) values and higher Langmuir constant b˜0.32L/mg for KTS-1 vs. 0.07 L/mg for KMS-1).

Example 2 Remediation of Hg²⁺, Cd²⁺, Pb²⁺, Cs⁺ and Sr²⁺ by K₂Sn₄S₉ andK₂Sn₂S₅

Materials and Methods.

Methods for making K₂Sn₄S₉ are described in detail in Marking et al., J.Solid State Chem. 1998, 141, 17-28, the entire disclosure of which isincorporated herein by reference. Methods of making K₂Sn₂S₅ aredescribed in detail in Liao et al., Inorg. Chem. 1993, 32, 2453-2462,the entire disclosure of which is incorporated by reference.

The ion-exchange experiments were carried out with the batch method. Atotal of 10 mg of KTS (1 or 2) was weighted into a 20 ml glass vial.Solutions of 2.5-3 molar equivalents (when compared to KTS-1 or KTS-2)of HgCl₂, PbCl₂, SrCl₂, CdCl₂, and CsCl were made. 20 mg of the KTS-1 orKTS-2 samples were weighed out into a 20 mL vial. 10 mL of theaforementioned solutions were added to the vial along with a magneticstir bar. The reactions were stirred overnight between 10-15 hours. Thestir bars were then removed, and the vials were centrifuged (3980 rpmfor 20 minutes). The supernatant was decanted into a centrifuge tubethrough a filter to collect any excess particles. The vials were thenwashed with water and centrifuged two more times. Finally, the systemwas washed once with acetone, centrifuged and decanted again. Thesamples were left to dry in a dessicator. The solids isolated with thefiltration were analyzed with energy dispersive spectroscopy (EDS) (Cs,Sr, Hg, Pb, Cd-exchanged materials). Each experiment was performed intriplicate.

The EDS analyses were performed using a JEOL JSM-6400V scanning electronmicroscope (SEM) equipped with a Tracor Northern EDS detector. Dataacquisition was performed with an accelerating voltage of 25 kV and 60 saccumulation time.

The results of the ion exchange studies are shown in Table 2.

TABLE 2 Ion-exchange of K₂Sn₄S₉ and K₂Sn₂S₅ with heavy metal ions (Hg²⁺,Cd²⁺, Pb²⁺, Cs⁺ and Sr²⁺) analyzed by SEM-EDS. Results for KTS-1 Resultsfor KTS-2 Ions Exchanged (K₂Sn₄S₉) (K₂Sn₂S₅) Hg(II) Exchanged, Hg₁Sn₄S₉Exchanged, Hg₂Sn₂S₅Cl₂ Cd (II) Exchanged, Cd₁Sn₄S₉ Exchanged: Cd₁Sn₂S₅Pb(II) Exchanged, Pb₁Sn₄S₉ Exchanged: Pb₁Sn₂S₅ Cs (I) Exchanged,Cs₂Sn₄S₉ Exchanged: Cs₂Sn₂S₅ Sr(II) Exchanged, Sr₁Sn₄S₉ Exchanged:Sr₁Sn₂S₅

Example 3 Remediation of Elemental Hg from Hydrocarbon Liquid UsingK₂Sn₄S₁₄

Materials and Methods.

Preparation of K₂Sn₄S₁₄: An amount of 1.10 g of K₂S, 4.72 g of Sn and4.1 g of S were mixed in a fused silica tube and the tube was evacuatedto 10⁻³ Torr. The tube was heated to 700-800° C. using a programmablefurnace to produce a liquid. The molten liquid was then pulled out ofthe furnace and cooled in air. The resulting material K₂Sn₄S₁₄ may becrystalline or amorphous or a combination of the two forms. K₂Sn₄S₁₅,K₂Sn₄S₁₈, K₂Sn₄S₂₀, and the like, can be prepared similarly by addingadditional amounts of sulfur in the reaction.

The Hg capture experiments were carried out with the batch method. Atotal of 10 mg of K₂Sn₄S₁₆ was weighted into a 20 ml glass vial. Asolution of Hg in hexane was made at a concentration of 1220 ppb Hgmetal. A volume of 50 ml hexane was used in each experiment. An amountof 45 mg of K₂Sn₄S₁₆ sample was added to the vial containing the Hghexane solution. The reactions were stirred overnight for a period of10-15 hours. The solid material was isolated by filtration and waswashed once with hexane. The solid samples were left to dry in adessicator. The solids isolated from the filtration were weighed andthen analyzed with energy dispersive spectroscopy (EDS) (Hg containingmaterials) using a JEOL JSM-6400V scanning electron microscope (SEM)equipped with a Tracor Northern energy dispersive spectroscopy (EDS)detector. Data acquisition was performed with an accelerating voltage of25 kV and 40 s accumulation time. Each experiment was performed intriplicate. The recovered solid material contained Hg along with K, Snand S. Removal of Hg was observed to be at least 98%.

Example 4 Remediation of Hg²⁺ Using BaSnS_(x)

Materials and Methods.

An amount of 3 mmol (0.714 g) of K₂S₅ was dissolved in 30-40 ml ofwater. To this yellow orange solution 1 mmol (0.260 g) of SnCl₄ wereadded and this was followed by the addition of 1 mmol (0.262 g) solutionof Ba(NO₃)₂ dissolved in 5 ml water. The mixture was distilled and theprecipitate was collected by filtration. Yield was >90% based on SnCl₄.Energy dispersive spectroscopy (EDS) elemental analysis on the yelloworange product indicated BaSnS_(x): where x=12-15.

In this experiment the Hg²⁺ ions were exchanging with Ba²⁺ ions. Atypical ion-exchange experiment of BaSnS₁₅ with Hg²⁺ ions is as follows:In a solution of Hg(NO₃)₂ (1.0 mmol) in 50 ml water, compound BaSnS₁₅ (1mmol, 737 mg) was added as a solid. The mixture was kept under magneticstirring or constant shaking for ≈2-12 h. Then, the dark brown or blackmaterial was isolated by filtration, washed several times with water,acetone and ether and dried in air. In all cases, the ion-exchange wascompleted after only one cycle. The removal of Hg ions from solution isquantitative.

Example 5 Simultaneous Hg²⁺ and Co²⁺ Removal Via Ion Exchange withNa₄Mg₂Sn₄S₁₂

Materials and Methods.

A mixture of Sn (1.9 mmol, 226 mg), Mg (1.1 mmol, 26 mg), Na₂S (2 mmol,156 mg), and S (5.2 mmol, 167 mg) was sealed under vacuum (10⁻⁴ Torr) ina silica tube and heated (50° C./h) to 670° C. for 48 h, followed bycooling to room temperature at 100° C./h. The excess salts were removedwith water to reveal yellow polycrystalline material K₄Mg₂Sn₄S₁₂. Theyield for this preparation exceeds 90% based on Sn as the limitingreagent. The same procedure can be followed for the synthesis ofK₄Mg₂Sn₄S₁₂ and Na₄Ca₂Sn₄S₁₂.

Powder of Na₄Mg₂Sn₄S₁₂ (180 mg, 0.18 mmol) was placed in an aqueoussolution (10 ml) of Hg(NO₃)₂ and Co(NO₃)₂ (0.8 mmol each). The mixturewas then stirred for 24 h. The powder turned black from yellow in colorand it was isolated with filtration, washed several times with water,acetone and ether. The total weight of solid after drying was 0.210 g.Energy dispersive spectroscopy (EDS) elemental analysis on the blackproduct revealed the average formula corresponding to“Hg_(1±x)Co_(1±x)Mg₂Sn₄S₁₂” (x=0.1) indicating nearly equal pick-up ofHg and Co ions. Based on the Na₄Mg₂Sn₄S₁₂ formula the removal of both Hgand Co ions was quantitative.

Example 6 Synthesis of Other Chalcogenides

Example preparation of K₂Sb₄S₇: An amount of 1.10 g of K₂S, 4.81 g of Sband 1.9 g of S were mixed in a fused silica tube and the tube wasevacuated to 10⁻³ Torr. The tube was heated to 600-800° C. using aprogrammable furnace to produce a liquid. The molten liquid was thenpulled out of the furnace and cooled in air. The resulting materialK₂Sb₄S₇ may be crystalline or amorphous or a combination of the twoforms. K₂Sb₄S₈, K₂Sb₄S₁₀, K₂Sb₄S₁₄, and the like, can be preparedsimilarly by adding additional amounts of sulfur in the reaction.

Example preparation of CaSnS₆: An amount of 0.72 g of CaS, 1.2 g of Snand 1.6 g of S were mixed in a fused silica tube and the tube wasevacuated to 10⁻³ Torr. The tube was heated to 600-880° C. using aprogrammable furnace to produce a liquid. The molten liquid was thenpulled out of the furnace and cooled in air. The resulting materialCaSnS₆ may be crystalline or amorphous or a combination of the twoforms. CaSnS₇, CaSnS₈, CaSnS₁₀, and the like, can be prepared similarlyby adding additional amounts of sulfur in the reaction.

Example preparation of K₄Mg₂Sn₄S₁₂: An amount of 2.22 g of K₂S, 4.71 gof Sn, 0.46 g and 3.5 g of S were mixed in a fused silica tube and thetube was evacuated to 10⁻³ Torr. The tube was heated to 700-850° C.using a programmable furnace to produce a solid. The material can beisolated by either cooling the furnace to room temperature over thecourse of 2-6 hours or by quenching in air by pulling the silica tubeout of the furnace. The material K₄Mg₂Sn₄S₁₂ is crystalline.

As will be understood by one skilled in the art, for any and allpurposes, particularly in terms of providing a written description, allranges disclosed herein also encompass any and all possible subrangesand combinations of subranges thereof. Any listed range can be easilyrecognized as sufficiently describing and enabling the same range beingbroken down into at least equal halves, thirds, quarters, fifths,tenths, etc. As a non-limiting example, each range discussed herein canbe readily broken down into a lower third, middle third and upper third,etc. As will also be understood by one skilled in the art, all languagesuch as “up to,” “at least,” “greater than,” “less than,” and the likeincludes the number recited and refers to ranges which can besubsequently broken down into subranges as discussed above. Finally, aswill be understood by one skilled in the art, a range includes eachindividual member.

It is specifically intended that the present invention not be limited tothe embodiments and illustrations contained herein, but include modifiedforms of those embodiments including portions of the embodiments andcombinations of elements of different embodiments as come within thescope of the following claims.

1. A method comprising: exposing a fluid sample comprising a metal to achalcogenide compound having the formula (A_(x)B_(x′))M_(y)Q_(z), whereA is an alkali cation or an alkylammonium cation; B is an alkaline earthcation; M is Sn, Zn, P, Cu or Sb; and Q is S or Se, wherein the valuesof x, y and z can be the same or different; x, x′ and y can range,independently, from 0 to 9, provided that if one of x and x′ is zero,the other is not; and z can range from 1 to 25, whereby the chalcogenidecompound absorbs the metal; and removing the absorbed metal from thefluid sample.
 2. The method of claim 1, wherein the metal is at leastone metal ion that undergoes ion exchange with the chalcogenidecompound, and further wherein the at least one metal ion is selectedfrom the group consisting of ions of Cs, Sr, Hg, Pb, Cd, Co, Ni, Cu, Au,Ag, Pt, Pd, and Tl.
 3. The method of claim 1, wherein the metal is aradionuclide ion.
 4. The method of claim 1, wherein the metal is anelemental metal.
 5. The method of claim 4, wherein the metal is mercury.6. The method of claim 5, wherein the fluid sample comprises a liquidhydrocarbon.
 7. The method of claim 6, wherein the metal is mercury andthe liquid hydrocarbon is petroleum or crude oil.
 8. The method of claim4, wherein the fluid sample comprises natural gas.
 9. The method ofclaim 1, wherein the fluid sample comprises both ionic and elementalmetal and further wherein ionic and elemental metal are removedsimultaneously from the fluid sample.
 10. The method of claim 1, whereinthe chalcogenide compound has the formula A_(x)M_(y)Q_(z), wherein A isan alkali cation, x and y are in the range from 1 to 9, and z is in therange from 1 to
 25. 11. The method of claim 10, wherein x is 1 or 2, Mis Sn or Sb; y is 2, 4 or 8; and z is in the range from 6 to
 23. 12. Themethod of claim 10, wherein the chalcogenide compound has a formulaselected from the group consisting of A₂Sn₄S₉, A₂Sn₂S₅, A₂Sn₃S₇, andA₂Sb₄S₇, and A is selected from the group consisting of K, Li, Na, K,Rb, and Cs.
 13. The method of claim 10, wherein the metal comprises Csor Sr radionuclide ions.
 14. The method of claim 1, wherein thechalcogenide compound has the formula B_(x)M_(y)Q_(z), wherein x and yare in the range from 1 to 9 and z is in the range from 1 to
 25. 15. Themethod of claim 14, wherein x is 1 or 2, M is Sn or Sb, y is 2 or 4, andz is in the range of 5 to
 25. 16. The method of claim 1, wherein thechalcogenide compound has the formula (A_(x)B_(x′))M_(y)Q_(z), where x,x′, and y are in the range from 1 to 9 and z is in the range from 1 to25.
 17. The method of claim 16, wherein x is 4, x′ is 2, M is Sn or Sb,y is 4, and z is
 12. 18. The method of claim 1, wherein at least 90percent by weight of the metal is removed from the fluid sample.
 19. Themethod of claim 1, wherein at least 98 percent by weight of the metal isremoved from the fluid sample.
 20. The method of claim 1, wherein thechalcogenide is selected from the group consisting of A₂Sn₄S_(z),BSnS_(z), and A₄B₂Sn₄S₁₂, where x is in the range from 4 to 25.